Southern Europe has a lighter industry than Northern Europe. At the same time, they have been an important importer of Northern European products. As such, they have sustained employment and profits in Northern Europe. However, light industry is not as valuable as our heavy industry. This has meant that we in Northern Europe have had to give them consumer loans to be able to continue buying our products to maintain our profits. Now that they can't afford this, they have to borrow from us to pay back the loans we gave them so they could maintain our profits in the first place.
Greece also maintains an enormously strong and therefore also expensive military (which Greece borrowed and borrows a lot from) as protection for Europe against the East. You can think what you want about the need for this protection, but the fact is that it is meant to be for our protection in Western and Northern Europe as well.
Then parts of the Greek public sector are inefficient. The tax system works poorly. But even if those things need to be reformed, nothing is solved by making the Greeks even poorer. Poor consumers cannot maintain enough purchasing power to sustain employment and profits.
Greece was highly leveraged even before the financial crisis that began in the US in 2008. But the loan situation only became unsustainable with the effects of that crisis on the world economy and Greece's economy.
Financial crises hit the world more frequently and harder since World Capital in the 80s began to try to reduce wage costs in relation to the profit share. The problem lies in: Poor consumers cannot consume enough to keep the economic wheels turning.
This has been solved by Kapitalet offering consumers consumer loans. But in the end the loans on the loans on the loans must be repaid. When this doesn't work, we get another financial crisis.
Nation states are best at democracy and welfare. But they need to work together to make sure that all countries and people do well economically, even if it may go a little better for some. If the differences are too great, we all suffer the consequences in the form of financial crises, lower profits, lower general purchasing power, terror, civil war, crime and mass unemployment.
Next, it may also be us who are affected. Sweden's public sector is low-leveraged, but the private sector is sky-high.
Then it is most important of all unfair and false mathematics that the poor should be so poor and the rich so ossified rich.